In vivo release of endogenous glutamate and aspartate in the rat striatum during stimulation of the cortex

The release of endogenous glutamate and aspartate from corticostriate neurons in the anaesthetized rat was investigated. Efflux of glutamate, aspartate and leucine in push-pull cannula perfusates of the striatum was measured in 1 min fractions collected before, during and after a 4 min stimulation period of ipsilateral frontal cortex. Efflux of the putative excitatory amino acid transmitters, glutamate and aspartate, determined during the first minute of stimulation, was significantly elevated above prestimulation resting level (by 167% and 316%, respectively), while efflux of leucine, a non-transmitter amino acid, remained unchanged. Efflux of glutamate and aspartate during the last 3 min of stimulation dropped rapidly, indicating the activation of a regulatory mechanism, presumably re-uptake. The data further support the hypothesis that glutamate and/or aspartate act as transmitters or are metabolites of transmitters in the corticostriate pathway.